In Star Trek, when was impulse drive developed? There seems to be an inconsistency. Zephram Cochrane first deployed Warp drive in 2061 with the assistance of chemical rockets, as detailed in Star Trek: First Contact. Is there any mention of Impulse drive prior to 2061? In Where No Man Has Gone Before, men had used impulse drive to reach the edge of the galaxy.
I have read non-canon explanations - if a warp drive moves the object by bending space, it would not be able to compensate between the relative velocity of its destination vs the trip origin, or delta v. As a ship traversed the galaxy, the differences in galactic orbital velocities would require significant delta v moving in any direction within the galactic plane (traveling straight "up" or "down" would not result in any direct change). Even returning to Earth 6 months later would result in a delta v of 60 km/sec as the Earth would be on the other side of the Sun heading in the opposite direction. However, I've never heard mention of this concept in Star Trek and the ships just appear to pop into orbit without necessitating an "impulse burn" to enter orbit.
Is there any canon explanation when or even why Impulse engines were developed? Was it developed after warp drive? There seems to be a discontinuity in the story line.